THE BREATHITT GROUP OF KENTUCKY AND THE ALLEGHENY FORMATION (GROUP) ELSEWHERE IN THE APPALACHIAN BASIN ARE OF EARLY PENNSYLVANIAN AGE
The Breathitt Group (Bee Rock, Grundy, Pikeville, Hyden, Four Corners, and Princess Formations) of eastern Kentucky and the Pocahontas, New River, Norton, Wise, and Harlan Formations of western Virginia comprise a northwestward thinning wedge of sandstone, siltstone, shale, coal, seat earth, limestone, and altered volcanic ash beds (tonsteins). Coal beds and marine beds have been well correlated and mapped in Kentucky, Virginia, and West Virginia, and the Fire Clay tonstein in the Hyden Formation and the equivalent part of the Pottsville Group has been traced through most of the central Appalachian Basin.
The Upper Banner tonstein (316.1± 0.8 Ma, Lyons, et al., 1997) and the Fire Clay tonstein (314.7± 1.1 Ma, Lyons et al., 2006 and 314.6± 0.9 Ma, Machlus et al., 2006) have been dated by high precision Pb-U methods. Extrapolation from the tonsteins has yielded consistent ages for coal and marine beds of the Breathitt Group. The Princess No. 9 coal bed (top of the Princess Formation of the Breathitt Group) (Upper Freeport coal bed of the Allegheny Group in Pennsylvania), has an extrapolated age of 311.9 Ma. The base of the Princess formation, the Stoney Fork Limestone Member, has an extrapolated age of 313.8 Ma. According to the USGS Divisions of Geologic Time the Bashkirian/Moscovian (or Conemaugh/Allegheny) boundary is at 311.7± 1.1 Ma, thus the Allegheny Group and all older Pennsylvanian strata are Early Pennsylvanian in age.